A blog by Harry Stein about public policy, with some DC sports thrown in.

Is the House in play if Trump wins the Republican nomination?

As Donald Trump appears poised for a big round of victories in today’s Super Tuesday primaries, his success is forcing everyone to rethink their assumptions about politics. One assumption to question is that gerrymandering gives Republicans a lock on the House of Representatives until the next round of redistricting after the 2020 Census. I’m not saying Democrats will win the House of Representatives if Trump is the Republican nominee, and I wouldn’t rule out the chance that Trump wins the White House, but I do think the House is in play this year.

After the 2012 election, Ian Millhiser looked at the results and found that Democrats would have needed to win the nationwide vote in House races by 7.25 percentage points to win control of the House. The actual outcome depends on separate races in the 435 Congressional districts, not the national vote totals, but the national vote provides a useful approximation of the kind of election it would take for Democrats to win the House. It’s worth pausing to note that Democrats did win the national House vote by a bit more than 1% in 2012, but because of gerrymandering that wasn’t nearly enough to win a majority of Congressional districts.

Ian notes that Democrats actually did win a nationwide House vote by more than 7.25% in recent history, with a 7.9% margin of victory in the 2006 wave. In 2008, Democrats won by an even larger margin of 10.6%. So it is certainly possible for Democrats to win the national House vote by more than 7.25%, but it would take a wave.

How would a wave play out if Trump is the nominee this year? First, Democratic voters turn out to vote in high numbers in response to the threat of a Trump presidency. With all of Trump’s inflammatory rhetoric, it shouldn’t be hard to convince Democratic voters that this election matters. Meanwhile, Republican voters in the #NeverTrump camp feel they don’t have a candidate, and stay home on election day.

Notice that this scenario does not require Republican voters to vote for Democratic House candidates, nor does it rely on the small number of true “swing” voters. It’s all about turnout. While turnout is influenced by the presidential election, it also impacts down-ballot races for the House and Senate.

Back in November, Kyle Kondik, the managing editor of Sabato’s Crystal Ball, floated the possibility that Democrats could win the House if Trump turns off enough Republican voters. And according to a recent CNN poll, which showed Trump with a commanding lead in the Republican primary, about a quarter of Republicans say they wouldn’t support Trump if he is the nominee.

However, the same CNN poll also found similar results for Republican voters saying they would not vote for Ted Cruz or Marco Rubio if they are the Republican nominee. Some of these numbers are probably inflated across-the-board for all the Republican candidates, with feelings running high in the heat of the primary. But these results may also suggest a Republican vulnerability that extends beyond the scenario where Trump wins the nomination. Some Republicans who say they will not support Cruz or Rubio might be dedicated Trump supporters. So there is also a scenario where Cruz or Rubio wins the nomination, but Republican turnout is still depressed in the general election as angry Trump voters spurn the Republican party and stay home.

Of course, it could play out differently. Maybe Trump mobilizes lots of Americans who otherwise wouldn’t have voted, and when they show up at the polls to vote for Trump, they also vote for Republicans down the ballot. Or maybe #NeverTrump Republicans come out to vote for a third party candidate, instead of staying home. Maybe both of those things happen, and Republican turnout hits record highs. Even if Republicans split their votes between two presidential candidates (Trump and a #NeverTrump candidate to be named later), a high overall turnout for Republican voters would still benefit Republican House and Senate candidates.

Republicans could certainly do very well in 2016. As of today, the betting market at PredictIt gives Republicans a 27% chance of winning both chambers of Congress and the White House in 2016. The craziness of the primaries might be resolved and forgotten by the time voters cast their ballots in the general election. Remember the “PUMAs” who said they wouldn’t vote for Barack Obama in 2008 because he wasn’t Hillary Clinton? Things that seem extremely significant now might be irrelevant later.

Winning the House would be a very tall order for Democrats. According to the Cook Political Report, Democrats would need to win their 170 safe seats, all 13 likely Democratic seats, all 4 leaning Democratic seats, all 16 tossups, all 13 seats that are currently leaning Republican, and even 2 of the 13 seats that are likely Republican in order to win the 218 seats required for a House majority.

In January, Stu Rothenberg said “you’d need a magnifying glass, probably even a microscope, to find the party’s chances of taking control.” As of today, PredictIt bettors give Democrats a 13% chance of winning undivided control of Congress and the White House. But that’s not 0%. As Jim Carrey would say, “So you’re telling me there’s a chance.”